The present invention relates to electronic engine controls for an internal combustion engine, and in particular to closed loop air-fuel ratio control.
Internal combustion engines are typically coupled to an emission control device known as a three-way catalytic converter (TWC) designed to reduce combustion by-products such as carbon monoxide (CO), hydrocarbon (HC), and oxides of nitrogen (NOx). Additionally, an exhaust gas sensor capable of providing a signal representative of an air-fuel ratio of an exhaust gas mixture exiting the TWC can be used in a closed-loop strategy to control the engine air-fuel ratio, providing fuel economy and emission control improvements over an open-loop strategy. Such sensors typically need to be heated above a predetermined temperature in order to operate properly. Therefore, in order to make measurements of the air-fuel ratio even when the exhaust gas temperature is low, some sensors are equipped with heaters which start heating up when the ignition key is in the xe2x80x9cONxe2x80x9d position.
The inventors herein have recognized a disadvantage with this approach. Namely, when the engine is first started, there is a certain delay before closed-loop air-fuel control strategy can commence associated with the time that it takes for the exhaust gas sensor to heat up. This delay reduces fuel economy and emission control. However, the inventors have recognized that under certain operating conditions, such as when the engine is temporarily shut off during idling, or decelerating, maintaining the power to the heaters can eliminate this delay in closed-loop control. Therefore, when the engine is restarted, the sensor temperature will be at the level required for proper operation.
This invention recognizes that the delay in the start of closed loop air-fuel control strategy can be reduced by maintaining the power to the exhaust gas sensor heaters during the time periods when the engine is temporarily shut off but the ignition key remains in the xe2x80x9cONxe2x80x9d position.
Accordingly, a system and a method of controlling an internal combustion engine coupled to an exhaust gas aftertreatment device, the device having a sensor coupled downstream of it, include: starting the engine; performing closed loop air-fuel ratio control after a first set of operating conditions has been met; stopping the engine; subsequently restarting the engine; and performing closed loop air-fuel ratio control after a second set of operating conditions different from said first set of operating conditions has been met.
According to another embodiment of the present invention, a system and a method for controlling an engine in a vehicle, the engine having an exhaust gas aftertreatment device coupled downstream of it, include: a sensor, comprising a heater, providing a signal indicative of an air-fuel ratio of an exhaust gas mixture entering the device; and a controller supplying power to said heater, providing a first indication that a first set of operating conditions has been met, and in response to said first indication adjusting an amount of fuel into the engine based on said sensor signal, discontinuing supply of fuel to the engine, maintaining power to said heater, resuming supply of fuel to the engine, providing a second indication that a second set of operating conditions different from said first set of operating conditions has been met, and in response to said second indication adjusting said amount of fuel of fuel into the engine based on said sensor signal.
An advantage of this invention is improved fuel economy. Another advantage of the present invention is improved emission control.
The above advantages and other advantages, objects and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings.